The human placenta secretes a growth hormone variant (placental growth hormone) in increasing amounts during pregnancy. Placental GH increases throughout pregnancy, and pituitary GH is suppressed as measured by conventional assays during the latter half of pregnancy, because of negative feedback on pituitary somato-trophs by placental GH. The objective of this study is to determine whether or not pituitary GH is detected by chemiluminescent assay during late pregnancy in healthy women.